The present invention relates broadly to methods and apparatus for disposing of hazardous waste material. More specifically, the present invention is directed to a method and apparatus for disposing of hazardous waste material while providing supplemental fuel for a cement-producing kiln.
Hazardous waste material is not necessarily toxic waste material which typically presents a chemical hazard, a nuclear hazard, or both, and its mere presence is dangerous for humans. Hazardous waste material, on the other hand, is waste material which consists of discarded plastics, rubber gloves, paper, paint filters, ground-up air filter material, and other such items which are unsuitable for human consumption or recycling. To be used with the present invention, however, the hazardous waste material must also contain some minimal fuel value that can be realized and applied through burning. The goal of the present invention is to recover and make use of the fuel value inherent in certain hazardous waste material, while simultaneously disposing of the material.
Portland cement, which is conventional cement, is manufactured in rotating kilns which are typically very large and very hot. Such kilns are often more than ten feet in diameter and several hundred feet long. The operating temperature of such a kiln is about 3,000.degree. to 4,000.degree. Fahrenheit. Cement kilns are mounted for rotation with the infeed at one end and the discharge at the other, with both ends closed by hoods. Portland cement is made by heating certain materials, primarily, limestone, in such a rotary kiln. After being fired at the high temperatures associated with the kiln atmosphere, the limestone, sand, ash, and water, which begins as a slurry or sludge, undergoes a chemical reaction at the elevated kiln temperature and becomes formed into rock-like material which is ground to dust to make the cement.
Such cement kilns are typically fueled by oil, coal, gas, or other conventional fuel material which is injected into the kiln. The present invention allows the efficient use of hazardous waste material as a supplemental fuel to provide several advantages. Among these are the reduction of primary fuel required and the destruction of the hazardous waste material while recovering the fuel value therefrom which would otherwise be lost if the waste material were merely buried in a landfill.
Attempts have been made in the past to incorporate the burning of hazardous waste material in cement production. In the past, kilns operated without water have been provided with openings into which buckets of the hazardous waste material would be dropped, bucket and all, to burn in the kiln. This method, while somewhat dangerous to personnel, often resulted in the incomplete burning of the hazardous waste material and the subsequent fueling of the kiln interior by unburned hazardous waste. Additionally, the buckets were wasted.
A further attempt was made to inject the hazardous waste material into the kiln using a pipe. Typically, the primary fuel is fed into the kiln through an extended pipe which creates a nozzle, in turn, creating a fire storm inside the kiln fueled by moving primary fueling material. A second burner tube was inserted adjacent the primary burner tube in the kiln and the hazardous waste material was injected through the secondary burner tube. This proved problematic as well because the bulk hazardous waste material would not fully burn in the atmosphere of the kiln resulting in inefficient use of the material. Further, the burner pipe eventually became clogged with unburned waste material along the inner wall of the tube. Therefore, the old method of injecting as much hazardous waste material into the kiln as could be forced through the tube resulted in the disposal of a portion of the hazardous waste material. However, the equipment used could not be effectively maintained over an extended operational period due to the aforesaid fouling by the hazardous waste material.